You know - weird, I'd actually never really thought about it -- I just assumed they were 17ish, and in their final year of high school. But you're totally right - why *would* Bender stay a second longer than he had to. (Especially when I think that he could have stopped Vernon's 'And that's another detention and that's another detention' with a simple 'I'm outta here.') The only thing I can think of, is that maybe he has more ambition than he seems to.